Photometer.



PATBNTBD JUNE 18, 1907. T.T0RDA.

PHOTOMETER.

APPLICATION FILED FEB. 26. 1906.

' 2 SHEETS-SHEET 1.

Winn 1| n u l Ill'lllmml PATENTED JUNE 18, 1907. T. TORDA.

PHOTOMETBR. y APPLIoATIoN FILED FEB. 2s. 190e.

2 SHEETS-sumar 2.

' ASW In uen for Imag/s.

IIIIIIiIIIII rIGII UNITED STATES PATENT OFFICE.

PHOTOMETER.'

Specification of Letters Patent.

A Patented June 18, 1907.

Application led February 26, 1906.- Serial No. 308,002.

which it appertains to make and use the.

same. y v

This invention which consists of improvements 1n photometers, for measurmg the intensity of a light source, such as that of electric incandescent lamps, arc lamps and the like, relates to those photometers which comprise a measuring or recording instrument and a light sensitive cell of selenium, the electrical resistance of which u )on being exposed from darkness to the .light rays is altered and recorded, the object ent invention being to provide such photometers with Ian automatic shutter arrangement by the use ofwliich the time of exposure is iixed and the correct amount of time for recu eration allowed after each exposure, not at t ekwill of the operator but entirely autoi-natically, the time of recuperation of the selenium cell being dependent upon the length of the previous ex vosure thus insuring a greater accuracy than has previously been obtained by apparatus of -this class.

One class of photometers hitherto in use have been based on the so called comparative method, using a standard'lamp. for com aring same With the one under test. his comparative photometry is very tiring, as

for each measurement the, operator mustapply his own judgment and' strain his eyes in the comparative observation, whereby a personal error comes into play, and the longer the testing lasts the' more; tired kthe operator gets and the more his errors increase, while at the Sametime the influence of the variations of the standard light affectseachv measurement and. causes repeated errors.

In the case of the presentimprovementsf the above disadvantages do not exist, 'asti/1e'.

reading is taken from a measuring 'instrument, and the use of' the standard` ;lanip comes into play only once, when the scale'of,` the direct reading instrument is permanently estabhshedby means ofa verycareful coniparative test.

of the pres-v In the case ofthe comparative photometry, great care also requires. to Abe taken to prevent the eyes Jfrom being exposed to the out- While 1n the ease of the usual desi ns of my improved photometer, the lam is uring the test, inclosed in a light tight ox which enables the measurements to be taken in broad daylight.

The use of the comparative photometer is irksome and demands a certain skill and knowledge from the operator, While in the case of my improved. photometer the reading being absolutely direct, requires no special knowledge. l

In order that my invention may be clearly understood and more easily carried into practice I have appended hereunto a sheet of drawings upon which I have illustrated the nature of my said invention;

Figure l is a diagram illustrating the schematic arrangement and connection of my photometers. trating the variation of the ohmic resistance in' terms of time exposure and rest in darkness of a selenium cell` Fig. 3 is an elevation of one form of automatic mechanism for side light, thereby necessitating a dark room,

Fig. 2 is a diagram illususe iny operation of same. Fig'. 4 is a plan i of Fig. 3. Fig. 5 is an end' elevationv of Fig. 3. Fig. 6 is a part elevation similar to that of Fig. 3 but illustrating the lever in the open position. i

With reference to Fig.-1 the selenium cell is placed .in the circuit of a constantk electromotive force,.so as to carry according to itsl dark resistance a. certain electricv current when the vsWitclrS Aclosesthe circuit, and which current produces a deflection on the galvanometer or milliampere .meter M A; Taking thisdeectionwhich corres onds to the dark resistance-asf zero point, t e measv urement of the-lighteffect is obtainedby'exposing the vseleniurncellS C to vthelight rays of the lampl L, and i through .the Alight effect' the resistance of ,thefseleniumi'cell S; C4 and l therewiththe;resistance of the. closed circuit,=.

will'decrease .according tothe value-of theA rl v meter M3 A-r -will then give greater. deflection;l ,With the. measuringfofthe Vdifference 1n; the..

agdirectr reading of the ting intensity in candle?powerfprfequalr g,; l the yschemat arrangement :land

.lighting intensity, fandv the I ",fmilfliampere.

.1015i j .deliections Y between the; :darkv and: `the flight y ex osedconditions, fligh v is thereby obtained@ f l in Fi connections of the selenium photometer is given, whereby S H represents the shutter, hereafter referred to, and by the operation of which I obviate the dil'liculty hitherto experienced in obtaining a practical and commercial selenium photometer and which has been due to the fact that the selenium when once exposed to the light effect takes along time before it regains its original dark resistance, so as to be suitable for a new exposure.

Fig. 2 illustrates the lcharacteristic curves of a selenium cell illustrating the retardation property, in regaining its 'original state. These characteristic curves 'represent the ohmic resistance, of the selenium cell in terms of both time of the exposure, and the rest in darkness required under a certain amount of light. The characteristic curve K indicates that at the time of opening the selenium cell, a very short time isY occupied in effecting a considerable alteration of the resistance and that a further exposure effects only a slight degree of variation of resistance.

The characteristic curve K also shows a more or less sharp bend, and this, together with the curve L indicates that an exposure reaching before or about tov the knee, will effect such a molecular stress in the selenium cell, that the same will regain in a comparatively short time of darkness. its original state, but if the selenium cell is' exposed such a length of ltime that the curve reaches b'eyond the knee to say point M of curve K,

then the molecular stress is so excessive that it takes many minutes or hours before it reaches its original point. l

Recognizing, and having ascertained the fact that a reading taken after a short or momentary exposure gives a reliable result, as regards the light e'ect, while it does not affect the molecular conditions of the selenium cell I therefore employ an automatic arrangement which fixes the necessary short I l exposure and terminates same through its automatic action, and fixes a certain time of restin darkness, to enable the cell to regain its original properties in order to be ready for a new reading. y

The main obj'ect of the automatic shutter S H in Fig. 1 is that the resistance alteration of the selenium cell, exposed from darkness to light, shall takeI place to a certain degree only, the time of exposure being governed by the permissible molecular stress; and by the' corresponding time ofrecuperation and the necessary time -oftaking a reading. on the galvanometer or milliampere meter. To obtain `the above conditions of short exposure and iixe'd time of rest in darkness, I employ an apparatus and automatic arrangement, a constructional example of which is hereafter described.

The light'tight box contains a selenium cell S C, constant electromotive force in the form of small cells, a small switch or press contact S, a galvanometer or milliampere' meter M A, auxiliary regulating resistances when required, and an automatic shutter with mechanical arrangement, as represented in Figs. 3, 4, 5 and 6 which illustrate one form of the automatic arrangement but to which, however, I `do not bind myself.

In the use of the apparatus the action is as follows A light source L is placed at a proper distance, before the screen which cov'ers the whole of the partition containing the selenium' cell, after which the switch S is closed in the cell circuit and at the same time the screen S H is opened, when the effect of the light upon the selenium cell causes a deflection on the milliampere meter to take place, the reading of which being taken the screen closes automatically. The deflection measured from the 'zero point indicates the lighting intensity upon a certain scale,

'the whole operation being completed in a few seconds.

With reference to the constructional sketch of the automatic shutter illustrated by Figs. 3, 4, 5 and 6, a .sitrong spring T actuates the spindle A through a smalll number cf cog wheels, in such a manner that the same makes a certain number of revolutions per minute. On this spindle A is fixed a hollow ring Wheel which is divided in two segments B and C by two slots D and D.

In the closed position of the shutter S H the actuating lever E having pivotin point F rests with its -pins H and H inside t e ring and opposite to the slot D.

For opening and putting into action the mechanism the free end of lever E is pressed down, then the pins H and H pass through .the slot D to the outside periphery of the ring,

which when released comes into rotation, owing to the effect of the spring. During this rotation, the pin H slides on the outer periphery of the ring segment C and keeps the screen open until the slot Dl comes opposite to the pin which drops into the ring.4

under the weight of the lever. After the screen is closed and the lever E is in a horizontal position, the pins H and H slide inside the hollow ring which is rotating, and during which rotation the opening of 'the shutter is prevented by the ring segment B until the motion of the ring B is stopped, when the block G of the ring comes against the pins H and H. f I

' It Will readily be seen 'that other instruments or appliances such as a mirror reflector, voltmeter, wattmeters, and the like may be -combined with my selenium hotometer, without the necessity of any su stantial alteration,`while the automatic device may be actuated by any suitable motive power.

What he claims vand desires to secure by Letters Patent is The improvements in'photometers or ap# IOO 851,124 t y a prising a timing device and a shutter in oom- In testimony whereofl he has affixed his -bination with a selenium oell, and current signature, in presence of' two witnesses. meter, whereby the selenium cell is exposed THEODORE TORDA to the light rays for a certain period, and

5 shut off for another period in the required Witnesses:

proportions, substantially for the purpose JOHN W. MACKENZIE,

herein set forth. ALBERT JONES. 

